Seriously? In the situations where people talk about microaggressions, it's one party acting in a certain way toward someone from an oppressed class that subtly devalues them in a way that ties into the oppression of that class. Out of context, one may see it as "not a big deal", but in the broader context of that class's oppression, and the frequency with which people of the oppressed class may experience microaggressions, it is a big deal.

In that case, there is one clear party who is being (subtly) aggressive.